In contrast to conventional surgery, which requires a relatively large incision in order to gain access to a surgical site within a body, endoscopic procedures utilize natural passages, or, alternatively, involve the formation of very small portals to gain access to the surgical site of interest. Accordingly, an endoscopic procedure is often referred to as “minimally invasive” or “closed” surgery. One advantage of performing a procedure endoscopically is that since the portions of the body that are cut are reduced, the portions of the body that need to heal after the surgery are likewise reduced. Still another advantage of endoscopic surgery is that it exposes less of the interior tissue of the body to the open environment. This minimal opening of the body lessens the extent to which its internal tissue and organs are open to infection.
Advancements in this field of “closed” surgery, such as arthroscopy and, more generally, endoscopic surgery, have led to the creation of numerous minimally invasive surgical cutting instruments. As noted above, in closed surgery, access to the surgical site is gained via one or more portals. As such, the instruments used in the surgical procedure must be sufficiently flexible, smooth and elongated to permit the distal ends of the instruments to reach the surgical site with minimal trauma to neighboring tissues. One end of the instrument, often referred to as the “distal end”, is designed to be positioned at the surgical site. The opposed end of the instrument, often referred to as the “proximal end”, extends out of the patient's body. The distal end of the instrument is typically provided with some type of working head designed to manipulate the tissue against which it is placed whereas the proximal end of the instrument is provided with a mechanism for the user to remotely control the working head.
Surgical cutting instruments for use in closed surgery—often referred as endoscopic “shavers”—are typically composed of a pair of concentrically disposed, close-ended, generally tubular members, more typically an elongated outer tubular member terminating in a distal opening or “cutting window”, i.e., an aperture situated in the distal region, on the distal end or side wall, or both, and an elongated inner tubular member, slidably and concentrically disposed in the outer tubular member, whose distal end is disposed adjacent the cutting window of the outer tubular member. The distal end of the inner tubular member typically has a surface or edge for engaging tissue via the distal opening in the outer tubular member and cooperates with the opening to shear, cut or trim tissue, a process often referred to as “resection”. For example, the inner tubular member may be rotatably driven about its axis from its proximal end by a handpiece having a small electric motor which is controlled by one or more finger actuated switches on the handpiece, one or more foot switches on a console supplying power to the handpiece, or some other analogous control means. Cut tissue can then be aspirated through the hollow lumen of the inner tubular member to be collected via a vacuum tube communicating with the handpiece. The distal end of the inner tubular member can be provided with a number of dimensions or configurations, depending upon the surgical procedure to be performed. Similarly, the opening in the distal end of the outer tubular member may be adapted to cooperate with the particular configuration of the distal end of the inner tubular member. For example, the inner and outer tubular members can be configured to produce side cutting or end cutting, or a combination of the two, to cut soft or bony tissues or combinations thereof. These various configurations are generally referred to in the art as “shaver blades”.
Coordinating inner and outer cutting windows of a shaver each have perimeters that are generally composed of two relatively longitudinal, straight or curvilinear edges connected at their proximal ends and distal ends by two relatively transverse edges. The configuration of the longitudinal edges, and to a lesser extent the transverse edges is determined by the intended use of the shaver. For instance, shavers intended for use on soft tissue will be provided with cutting windows configured for increased resection efficiency but relatively low resistance to deformation since the cutting forces are typically low. Conversely, those shavers intended for use on tough tissue, such as meniscus or vertebral discs, will be provided with a greater resistance to deformation since the cutting forces are quite high.
The inner and outer tubular members are generally metallic and typically have at their proximal ends plastic hubs mounted thereto. The proximal ends of the metallic tubular members are typically knurled (i.e., manufactured, typically via a lathe, to include diamond-shaped or criss-cross pattern that is cut or rolled into metal). The tube and hub components are assembled together by heating them with an induction heater and then forcing the tubular component into the lumen of the hub such that the plastic is melted and bonds to the knurled portion of the tube. While this bonding method is in common use, it has drawbacks in that it requires an induction heater and complex affixture for aligning the distal end of the tubular member with the lumen of the hub, and for ensuring that the hub is properly positioned axially on the tube. The axial (or longitudinal) position is particularly important since skewed alignment and/or improper positioning may make the shaver inoperable.
As noted above, resection of tissue by a shaver blade is typically accomplished by cooperative interaction between the edges of the inner and outer cutting windows. As the inner and outer windows come into alignment, vacuum within the lumen of the inner tube sucks tissue into the opening formed. Continued rotation of the inner member causes the inner cutting edges to approach the outer cutting edges. Tissue in the cutting window between the inner and outer edges is either trapped between the edges or ejected from the window. Tissue trapped between the edges is either cut by the edges as they approach each other or torn by the cutting edges as they pass and rotate away from each other. The resected tissue is aspirated from the site through the inner lumen of the inner tube.
To produce an efficient cutting action, the clearance between the inner and outer tubular members is necessarily quite small, generally on the order of 0.2 mm (0.008 inches) or less as excessive clearance can result in tearing rather than cutting of tissue. However, lateral forces caused by cutting of tissue, particularly dense fibrous tissue like meniscus, may cause deflection of the inner tubular member within the outer tubular member so as to allow contact between the inner and outer cutting edges. This contact causes the cutting edges to dull, and more importantly, may generate metallic debris that is then deposited into the surgical site, with negative consequences to the patient. Metallic debris may also be created through rubbing contact between the distal portions of the inner and outer tubes in close proximity to the cutting windows during high-speed operation. Such rubbing may cause galling and cold-welding of the elongate metallic members in the regions in contact. In severe cases, galling may cause welding of the inner and outer members so as to make the shaver unusable.
To prevent such dulling, galling and welding, materials of the inner and outer distal ends are carefully selected and the components hardened and machined to very precise shapes, frequently with form tolerances of as little 0.0002 inches. The surface finishes of the bearing surfaces are also critical since irregularities in the surfaces can lead to high-localized stresses which, in turn, can result in galling of the surfaces during use. To address this issue, some manufacturers coat the inner member bearing surface with a gall-resistant metallic material, while others make the distal end of the inner member from a gall resistant alloy. In any event, galling and metallic debris created by shaver blades is still a frequent problem since inspection of the inner surface of the outer member is very difficult and minor manufacturing abnormalities can create surfaces which are not to specification. Because of these and other factors, forming of the inner and outer distal end bearing surfaces is a significant portion of the shaver blade manufacturing costs.
Another art-recognized manufacturing hurdle involves shaping and bending of the distal portion of the device. Access to certain structures during endoscopic surgery of knees, shoulders or other joints may occasionally be difficult, particularly when using a standard shaver blade. Because of this, endoscopic shavers are often configured with a distal portion that is angularly offset from the axis of the shaver handpiece and proximal portion. With shaver blades and burs having an angularly offset distal portion, surgeons can access portions of the anatomy not readily reached with standard unbent shavers. The distal portions of these devices are usually formed to the desired angular offset during manufacture, with typical offsets being on the order of twenty degrees or less. Bending fixtures and dies are used to produce repeatable bends with small radii. Other powered endoscopic devices, like the Merlin line of shaver blades available through Conmed (Utica, N.Y.), are supplied to the surgeon without an angular offset but allow the surgeon to bend the device to the desired offset in the operating room with the aid of an included bending device capable of producing a large bend radius that is distributed along the distal outer tube.
Critically, devices are generally supplied as either pre-bent or bendable in the field, but not both (i.e., pre-bent devices that are then further bendable in the field). The elongate tubular sections used for the distal portions of endoscopic shavers and burrs have uniform structural properties throughout their length. Bending of the tubular section during manufacture allows the use of dies and other tooling that are able to repeatably produce bends having a small radius. Attempting to modify the angular offset of such a pre-bent blade would be expected to result not in modification of the original bend, but in bending at locations on the tubular member adjacent to the bend produced during manufacture. Bending of the tube during manufacture work-hardens the material in the bent region so that any attempt to modify the bend will cause adjacent regions which have not been work-hardened to deform. For the same reason, bendable products like the Conmed Merlin shaver blade are formed with large bend radii so that significant work-hardening of the tubing does not occur. These bendable devices can be bent to an initial angular offset and then to another offset; however, the large bend radii severely limits the utility of these bendable devices. To access most structures, it is necessary that the bend have a small radius and be positioned near the distal end of the shaver blade.